1. Field of the Invention
The present invention relates to an image forming device such as a digital color copy machine or a pr a density correction method, and a non-transitory computer readable storage medium storing a program. Particularly, the present invention relates to a technique for correcting print density.
2. Description of the Related Art
For printing using an image forming device, in some cases, a problem is variation in print density due to individual difference, or due to time-dependent deterioration of an individual device. For such a problem, a technique has been known such that a density correction pattern is formed on an image carrier, such as a photoreceptor or an intermediate transfer belt; the density correction pattern is read by a density sensor of a device; and density correction is executed by using the read density value.
For example, Patent Document 1 (Japanese Patent No. 4383622) discloses the following technique. First, a gradation pattern for density correction is printed on a paper sheet by using a printer. A density correction table is created by reading the gradation pattern by using a scanner. Subsequently, patches are formed on an image carrier. The number of the patches is the same as levels of the density, which is corrected by using the scanner. The patches formed on the image carrier are read by an internal sensor. Then, a density correction table 1 is created by correcting the previous density correction table. Further, patches are formed on the image carrier. Here, the number of the patches is greater than the levels of the density, which is corrected by using the scanner. The patches formed on the image carrier are read by the internal sensor, and thereby a density correction table 2 is created. According to the technique disclosed in Patent Document 1, the density correction table 1 and the density correction table 2 are used, while they are switched with each other.
However, in an image forming device according to related art, detection accuracy is not necessarily good. When the detection accuracy does not match the density stabilizing performance of the device, excessive correction or a level difference in gradation occurs. Patent Document 1 does not consider such a problem.